350 gas mileage, same 10mpg city AND highway

Out in the back seat of my '60 Chevy
Workin' on mysteries without any clues..

Sorry... My Chev went from 17 to 20 mpg with no changes other than breaking it in, which took what seemed like an eternity. Oh and pump up the tires. I had a tire down to 15 lbs. not long ago but I hadn't noticed it and my mileage took a dump.

 

I put the same engine in a 78 GMC, was pulling about 8 mpg. Same scenario, rebuilt Q-jet. Ran good, I tore the carb apart, couldn't find a problem. Finally pulled the (wrong) Q-jet off my old 454 one ton, and the mileage doubled. See if you can find, or borrow another carb to try. Check your fuel pressure too. Too much pressure could be pushing excess fuel through.

 

I like to set the timing with a vacuum gauge and drive with one as well.....check ****** for slipage and see if it goes up on rpms before moving....might check plugs to see how their burning......and check springs in dist

 

As usual some really good sound advice an a bit of pie in the sky stuff.

I agree with Highway 41 in that you need to check the things that should be checked before you start swapping parts.

Go back and check the timing and then check it with the advance hooked up. Make sure the advance is working correctly and advances the total timing where you need it. That also means check the mechanical advance to make sure it works right.

Do as Hoop98 suggested and check the power piston on the QJ to make sure it is working correctly.

I'm not familiar with the ignition setup you have but it has always been a quandary to me why a guy will put a fancy race ignition on a basically stock engine for the street with no other modifications and no intention of racing the car.

Lastly, make sure all of the non engine variables are set right for the best chance at improving gas mileage. that includes making sure that the car is in alignment so you aren't dragging the tires due to excess toe in or toe out. Make sure that the air pressure is correct in all four tires. Not for cushy ride but for the best all around mileage and ride. As someone mentioned, brakes that are adjusted too tight will drag on the drums and cost mileage but that doesn't mean back them up so far that you don't have good pedal or the rig doesn't stop well.

 

I've got one of those 190 hp crate engines in my A on 32 rails. It weighs 1200kg (about 2600lbs) and about the best it did in the US was 14mpg. I found it only had about 24 degrees total timing dialled in and in now runs better nearer 30- someone else above posted the low compression needs more timing and that sounds right.

 

Had an OT pickup with a similar problem - ran fine but really lousy mileage. I spent months try this and that, & finally on the third carb teardown I discovered that the tip of one of the metering rods was bent. It was just bad enough that it wasn't seating in the jet - it wasn't at all obvious & was pure luck that I found it. Mileage jumped from 8 to about 14.

 

You will need around 52-54 deegrees advance at crusing rpm to get good mpg.
I'm getting 22mpg in my 65 chevelle with 305 and no od. You should be able to get high teens, at least.
Fix timing first and then lean out the carb.

 

main well plugs leaking??

 

That's a good point to make and different to my earlier point about WOT timing. I had an OT LS1 which would pull 45-47° advance at light cruise, but you can run into problems with a V8 distributor engine with that sort of timing. This is because the plug lead terminals are only 45° apart in the distributor cap and so you can get cross-firing resulting from big advance.

 

hadn't thought about this issue, good to realise it! 52-54* sounds like a lot of advance.

 

Fine tuning should help some but that engine is a slug. (no offence intended, you didn't build it.) A 350 with better compression and cam isn't working as hard to do the same job, pulling a heavy car down the hwy.

 

Let's see if we can put some scale or context on how bad your problem is.
At 60 MPH your aero drag is about 15 and drivetrain road losses are about 13 so say 30 HP to move it 60 MPH. At 10 MPG you are burning 6 GPH at 60 MPH, or about 37 Pounds per hour, or 1.232 pounds of gas per horsepower hour.

Here is a chart of a typical Pre Variable Valve Timing Pushrod type gas engine:



Your engine well tuned at Freeway speeds should be able to achieve somewhere in the yellow zone below. So we are using about 50 pct excess fuel.
The timing spec for a low compression 1969 350 was
4 Intial
28 Mechanical
24 Vacuum at 16 inches of vacuum.

As noted above that would be 56 in the stall, on the road it would depend on the load.

I would imagine you are way off on both advance and fuel and it's fixable.

Nothing new here, restating what others have said but I hope the chart shows you how MPG = Efficiency of Fuel Burn per HP hour (BSFC).

 

http://www.fueleconomy.gov/feg/bymake/Chevrolet1986.shtml

You guys that think this 190hp 350/350 with 308 rear gear can get better than 11 mpg are smoking crack !!!

The link has the mpg from factory info .
The 5.7s that are hitting 11 are doing it with OD and an ECM with less weight.

It's not going to happen ever at 16 mpg with a 350 and 308.
Tune it , time it, tweak it as much as you want it's not going to happen.

The 305 HO with OD in a lighter car got close.
The 4.3 and 3.8 In a much lighter car with OD got better than 16.

Once they dropped the compression to lower emissions the economy went out the window.

My 66 Pontiac 4 spd and 308 got 17 and would fry the tires right off . Lots more power than 190 hp.

Today's standard 2.4l 4 banger puts out 190 hp and gets close to 30 in light weight car.
No way in hell are you going to drag/feed 4 extra cylinders at larger displacement for same power and no OD with more weight going to hit 1/2 that with 15 mpg.
Quit drinking the bong water

 

That's funny. According to your link, the only 5.7 that gets mileage that low is in a C20 3/4 ton truck, which has a curb weight nearly 2000 lbs more than a '60 Chev sedan.

 

I call BS on that. Why? Because I have done exactly what you say is impossible. With more than 1 heavy car.

 

Look for all the 5.7s there's plenty and the 11 range is normal

http://fueleconomydb.com/index.php?...skip=40&-mode=list&year==1985&make==CHEVROLET

Here's some more
85 monte 305 with OD 14 mpg.

 

I've done it too !
But not with a 190 hp 350 mated to a th350 with 308.
That 190 350 needs A OD trans and 3.4 or numerically higher gear.
Or the th350 and 308 needs more Hp.

 

We are talking Highway MPG,

The first 350 I saw was 18;



Of course the 85 has OD but it has 18 pct more weight.

If you look at my yellow 60 MPH band above, does that look like a crack user?

Hoop

 

No crack/beer/dope/booze/tin foil hat/ or even soda pop. If the OP is right at 10 mpg right now, the mega tuneage & syntech oils will gain 2-3 mpg. A more (ready for it?) TRADITIONAL 283/327 freshie will be a vast improvement in every way. Who's doin' 8 ball's? Dat dirty hippie!

 

The 85 does have OD but also fuel injection and around 60 more HP.

 

What did the stock car get back then in terms of gas mileage and go from there.

And for an example, my stock '67 Camaro, 350SS/RS with an M-20 and a 3.31, 12-bolt posi- with 25.5" tall tires new got like 17 on the road.

I had my Buddy, "Nuts", install the great old -151 hy-cam in it and I went down to like 16 mpg...

I put my old junk301, -097 solid lifter cam and dropped down to like 15.5 or so, but I drove the dog-sh*t outta it..

Next, I never got any mpg readings out of the old hopped up 421/409 "W" engine, but I figured about 10 mpg.

Later, I installed my "Strong-Arm" 406 SBC in the '80's and it got right at 15 mpg running 55 mph on the hwy...

Something isn't right if you can't get stock mpg out of her???

pdq67

 

Kinda hard to do that, pdq67. No '60 350s to compare it to.

 

We shouldn't forget the original post 10 City maybe, 10 City and 10 Hwy with a 3.08 gear, Houston we have a problem.

Here is a 72 350 Impala, same basic powertrain, but considerably heavier and bigger overall. "Potentially" the 60 with the same basic powertrain, should be better.

I had to fight owners over EPA mileage for years and I figured out what to look for.

14.7 or leaner at cruise, normal coast down, full timing, in high gear they would always beat the EPA number at 55 Cruise which was the speed limit then. We had the hang on the window 1/10 gallon tester.

A 17 rated Riviera would get 21 at steady 55 (The National Speed limit), if you drove it at 65 on normal roads it got 16, if you 75 in and out of traffic dodging semis you got 13.

 

Thanks hoop98- that chart tells a story- you can see why diesels are so much better on light load...

 

Thays what I was thinking, I drive my 454 dully as my every day driver, I get about 14 on the hiway, and 11 around town. Mine is a '95.

I have to agree with everybody on the '60 start with a fine tune, the Q jet should do better then what he's getting.

 

My 3300 lb. coupe with a 11.3-1 383 got 10 mpg @75-90 mph with 4:88s 31"tall tires and a .64-1 overdrive!

 

Shows how important it is to get to that point where you are in the throttle but staying below the power circuit trigger point.

Upshifts and OD's are your wallets friend

Hoop

 

I have a 71 Lincoln Mark 111 460/365 hp
around town 16 mpg if I drive it on the Highway
at a Speed of 65 I can get 20 mpg
anything after that & I loose Gas milage like Crazy
I used to go Cross country a lot & Cruse at 85
so the Gas milage would be a lot less about 16
forget to mention it comes with Factory Dual Exhaust

Just my 3.5 cents

 

oh I forgot to say the Car weight is 5000 lbs

just my 3.5 cents

 

My '70 Chevelle convert. with orig. 350-300, [bought it new] in the early '70's would get 18mpg or so highway..It trended downward over the years, with a fresh stock rebuild [other than change to L-79 cam], orig. 4 speed and 3;31 gears it stayed around 17-18 til the gasoline quality got so bad..With stock Q-jet and all components in excellent shape I can get maybe 15.5 out on the road...Gas not formulated for old style carb fed engines is a lot of the trouble I think, though mid '70's low compression smoggers were horrid per gas mileage..